A clinical study was conducted using histological slides of all cases diagnosed as carcinoma of the thyroid in the United Birmingham (England) Hospitals since 1940 and in the Regional Histological Collection from 1953-67. A total of 23 patients or 8% were found to have medullary carcinonma. This type is histologically distinct being the only type to contain amyloid in the stroma. The clinical features of the patients treatment pathological findings histological findings and course of the disease are discussed and tabulated. Microscopic photographs from 6 of the cases are presented. Medullary carcinomas are of intermediate malignancy but tend to metastasize to cervical and mediastinal glands at an early stage. They do not respond to external irradiation or radio-iodine. Prognosis following surgery however is good. Total thyroidectomy and regional clearance of any involved glands is the treatment of choice.